In a conventional form of aerosol valve assembly, a vertically acting aerosol valve is opened to release product in the aerosol container by downwardly depressing a button or cap attached to the top of the upstanding stem of the aerosol valve. When the button is released, the valve is closed by a spring acting on the valve. The valve body positioned at the lower part of the valve stem has an upper horizontal continuous sealing surface circumferentially surrounding the valve stem. This upper horizontal surface, when the aerosol valve is closed, is urged upwardly into sealing relation against the valve sealing gasket by the spring acting on the valve body. One or more orifices in the valve stem are positioned above the lower surface of the valve gasket when the valve is in the closed position. The valve stem passes through a central opening in the gasket, and the circumferential surface of the central opening may provide a radially acting, secondary seal of the valve stem when the valve is closed. When the valve is opened by pressing the button, the valve stem moves downwardly and its one or more orifices will move to a position below the gasket. Product in the aerosol container may now, under the influence of propellant, pass upwardly through the conventional dip tube into the valve housing which surrounds the valve stem and valve body, then upwardly to flow over the upper horizontal surface of the valve body circumferentially surrounding the valve stem, through the one or more orifices into the valve stem, upwardly through the valve stem, and outwardly through an outlet nozzle in the button or cap attached to the top of the valve stem.
The above-described conventional aerosol valve is used to dispense many products including, in aspects particularly relevant to the present invention, products having powder suspended in a liquified propellant. Such products include antiperspirants, deodorants, foot sprays, etc. Unfortunately, the action of the conventional aerosol valve is compromised by powder build-up on the aforedescribed upper horizontal sealing surface of the valve body when the powder product is released from the aerosol container. This powder accumulation interferes with the full resealing action of the valve by causing the valve to be held partially open after the button is released. The result is that the aerosol container loses pressure even when not in use, and the propellant leakage can impair or destroy the usefulness of the pressurized container after a few operations of the valve. The problem is further exacerbated in the circumstance where modern day high powder loading is desired in the product to be dispensed, for example fifty-sixty percent solids by weight in the case of certain powder antiperspirants where the solids include the powder and other solids in the formulation.
Attempts have been made to overcome the above problems of powder valves, one such instance being disclosed in UK Patent Specification 1216655 wherein a plurality of concentric ribs with sharp top edges are placed on the aforesaid top horizontal sealing surface of the valve body (or on the lower gasket sealing surface) to encircle the valve stem. The sharp top edges cooperate with the gasket to form the valve sealing surfaces, and when powder product is released by actuating the valve, powder build-up is intended to occur inside of, outside of and in the valleys between the concentric ribs rather than at the tops of the ribs. However, powder can still accumulate sufficiently in the valleys to ultimately interfere with the valve sealing action.
A further attempt to overcome the above problems of powder valves is disclosed in U.S. Pat. No. 3,773,064, wherein a circumferential groove surrounds the valve stem with the orifices lying in a conical outwardly tapering section at the top of the groove and the sealing gasket fitting within the groove and around the conical section. A protruding cylindrical ridge in the groove presses into the gasket to enhance sealing. However, the compound surfaces including the bottom of the groove still present opportunities for powder build-up in the design, particularly under present day requirements for powder products having heavy loading of solids.